JEE Main & Advanced Sample Paper JEE Main Sample Paper-41

  • question_answer
    The value of \[\int_{-1}^{1}{\frac{d}{dx}}\left( {{\tan }^{-1}}\left( \frac{1}{x} \right) \right)dx\]is

    A)  \[\frac{\pi }{2}\]                                

    B)  \[\frac{\pi }{4}\]

    C)  \[-\frac{\pi }{2}\]                  

    D)  None of these

    Correct Answer: B

    Solution :

    Since, \[\frac{d}{dx}{{\tan }^{-1}}\left( \frac{1}{x} \right)=\frac{d}{dx}{{\cot }^{-1}}x=-\frac{1}{1+{{x}^{2}}}\] \[\therefore \]\[\int_{-1}^{1}{\frac{d}{dx}\left( {{\tan }^{-1}}\left( \frac{1}{x} \right) \right)}dx\] \[=-\int_{-1}^{1}{\frac{1}{1+{{x}^{2}}}}dx\] \[=-2\int_{0}^{1}{\frac{1}{1+{{x}^{2}}}}dx=-2[{{\tan }^{-1}}x]_{0}^{1}\] \[=-\frac{\pi }{2}\]


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